In mattress arrangements, such as in a bed arrangement or other seating or furniture arrangements, a support is provided to act on the weight or part of the weight of a user, wherein the bed distributes the weight from the body of the user over a part of a surface of the device. Depending on how the bed distributes the weight of the user, the bed will appear as being either soft or firm. The degree of firmness of such a bed is dependent on the properties of the elastic elements, such as the spring constant, and how the elastic members have been mounted in the bed, such as the degree of clamping or pre-tensioning. Thus, the firmness of the bed is normally set at the manufacturing of the device.
However, different persons wish and require different firmness. Further, different body parts may require different firmness.
It is known to provide bed arrangements with variable firmness. By inducing deformation to the elastic members to different degrees, the firmness of the device is adjustable. The deformation member has the ability to deform the elastic member independently from the deformation of the elastic member induced by the being. This means that the firmness of the bed is adjustable during initialization, according to the wishes of the user. It is also possible to compensate the firmness of the device for possible changes in the elastic properties of the elastic arrangement over time. Such known solutions are e.g. disclosed in EP 2 245 967 and WO 2009/120270.
Further, it is known to provide variation in firmness of a mattress by arranging coil springs on support plates having variable height. The height of the support plates may be controlled by rotatable elements arranged under the support plates, and having an off-centre rotation axis. Hereby, by rotation of the rotatable elements, the plates assume various height positions. Such firmness adjustment means are e.g. discussed in U.S. Pat. No. 3,340,548 and US 2011/0258772. It is also known to use a similar arrangement with support plates having variable height where the height of the support plates may be controlled by displacement members in the form of linear motors, jacks, and other types of lifting mechanism. Such firmness adjustment means are e.g. discussed in AU 55 13 00, U.S. Pat. No. 4,222,137, US 2006/0253994, WO 99/65366 and EP 2 245 967.
However, common problems with these previously known bed arrangements with variable firmness are that they are relatively complex, heavy and costly to produce. Further, these known bed arrangements are also often relatively difficult and cumbersome to use. Further, even though these known bed arrangements provide a certain degree of adjustability, this is often inadequate for the users' needs.
Another approach is presented in U.S. Pat. No. 8,176,589, by the same applicant as in the present application, in which the bed has a variable width, and the mattress is arranged to be expanded/contracted together with the expansion/contraction of the bed frame. However, a significant drawback of this approach is that the size of the bed varies significantly.
It is therefore still a need for a mattress arrangement, and in particular a bed arrangement, with adjustable firmness which alleviates the above-discussed problems.